The present invention is directed, in general, to a process for the preparation of taxol and other taxanes, and in particular, to such a process in which the C(7) or C(10) hydroxyl group of a taxane is selectively derivatized.
10-DAB (1), which is extracted from the needles of taxus baccata L., the English yew, has become a key starting material in the production of taxol and Taxotere, both of which are potent anticancer agents. Conversion of 10-DAB to taxol, Taxotere(copyright) and other taxanes having antitumor activity requires protection or derivatization of the C(7) and C(10) hydroxyl groups followed by esterification of the C(13) hydroxyl group to attach an appropriate side chain at that position. 
Until now, strategies for the preparation of taxol and taxol analogs were based upon the observation of Senilh et al. (C.R. Acad. Sci. Paris, II, 1981, 293, 501) that the relative reactivity of the four hydroxyl groups of 10-DAB toward acetic anhydride in pyridine is C(7)xe2x80x94OH greater than C(10)xe2x80x94OH greater than C(13)xe2x80x94OH greater than C(1)xe2x80x94OH. Denis, et. al. reported (J. Am. Chem. Soc., 1988, 110, 5917) selective silylation of the C(7) hydroxyl group of 10-DAB with triethylsilyl chloride in pyridine to give 7-triethylsilyl-10-deacetyl baccatin (III) (2) in 85% yield. Based upon these reports, in those processes in which differentiation of the C(7) and C(10) hydroxyl groups is required (e.g., preparation of taxol from 10-DAB), the C(7) hydroxyl group must be protected (or derivatized) before the C(10) hydroxyl group is protected or derivatized. For example, taxol may be prepared by treating 10-DAB with triethylsilyl chloride to protect the C(7) hydroxyl group, acetylating the C(10) hydroxyl group, attaching the side chain by esterification of the C(13) hydroxyl group, and, finally, removal of protecting groups.
It is known that taxanes having various substituents bonded to either the C(10) or the C(7) oxygens show anticancer activity. To provide for more efficient synthesis of these materials, it would be useful to have methods which permit more efficient and more highly selective protection or derivatization of the C(10) and the C(7) hydroxyl groups.
Among the objects of the present invention, therefore, is the provision of highly efficient processes for the preparation of taxol and other taxanes through selective derivatization of the C(7) group or the C(10) hydroxyl group of 10-DAB and other taxanes, particularly a process in which the C(10) hydroxyl group is protected or derivatized prior to the C(7) hydroxyl group; and the provision of C(7) or C(10) derivatized taxanes.
Briefly, therefore, the present invention is directed to a process for the acylation of the C(10) hydroxy group of a taxane. The process comprises forming a reaction mixture containing the taxane and an acylating agent which contains less than one equivalent of an amine base for each equivalent of taxane, and allowing the taxane to react with the acylating agent to form a C(10) acylated taxane.
The present invention is further directed to a process for the silylation of the C(10) hydroxy group of a taxane having a C(10) hydroxy group. The process comprises treating the taxane with a silylamide or a bissilylamide to form a C(10) silylated taxane.
The present invention is further directed to a process for converting the C(7) hydroxy group of a 10-acyloxy-7-hydroxytaxane to an acetal or ketal. The process comprises treating the 10-acyloxy-7-hydroxytaxane with a ketalizing agent in the presence of an acid catalyst to form a C(10) ketalized taxane.
The present invention is further directed to a taxane having the structure: 
wherein
M is a metal or comprises ammonium:
R1 is hydrogen, hydroxy, protected hydroxy, or together with R14 or R2 forms a carbonate;
R2 is keto, xe2x80x94OT2, acyloxy, or together with R1 forms a carbonate;
R4 is xe2x80x94OT4 or acyloxy;
R7 is xe2x80x94OSiRJRKRL;
R9 is hydrogen, keto, xe2x80x94OT9, or acyloxy;
R10 is hydrogen, keto, xe2x80x94OT10, or acyloxy;
R13 is hydroxy, protected hydroxy, keto, or MOxe2x80x94;
R14 is hydrogen, xe2x80x94OT14, acyloxy, or together with R1 forms a carbonate;
RJ, RK, RL are independently hydrocarbyl, substituted hydrocarbyl, or heteroaryl, provided, however, if each of RJ, RK and RL are alkyl, at least one of RJ, RK and RL comprises a carbon skeleton having at least four carbon atoms; and
T2, T4, T9, T10, and T14 are independently hydrogen or hydroxy protecting group.
Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.
Among other things, the present invention enables the selective derivatization of the C(10) hydroxyl group of a taxane without first protecting the C(7) hydroxyl group. Stated another way, it has been discovered that the reactivities previously reported for the C(7) and C(10) hydroxyl groups can be reversed, that is, the reactivity of the C(10) hydroxyl group becomes greater than the reactivity of the C(7) hydroxyl group under certain conditions.
Although the present invention may be used to selectively derivatize a taxane having a hydroxy group at C(7) or C(10), it offers particular advantages in the selective derivatization of taxanes having hydroxy groups at C(7) and C(10), i.e., 7,10-dihydroxy taxanes. In general, 7,10-dihydroxytaxanes which may be selectively derivatized in accordance with the present invention correspond to the following structure: 
wherein
R1 is hydrogen, hydroxy, protected hydroxy, or together with R14 or R2 forms a carbonate;
R2 is keto, xe2x80x94OT2, acyloxy, or together with R1 forms a carbonate;
R4 is xe2x80x94OT4 or acyloxy;
R9 is hydrogen, keto, xe2x80x94OT9, or acyloxy;
R13 is hydroxy, protected hydroxy, keto, or 
xe2x80x83R14 is hydrogen, xe2x80x94OT14, acyloxy or together with R1 forms a carbonate;
T2, T4, T9, and T14 are independently hydrogen or hydroxy protecting group;
X1 is xe2x80x94OX6, xe2x80x94SX7, or xe2x80x94NX8X9;
X2 is hydrogen, hydrocarbyl, substituted hydrocarbyl, or heteroaryl;
X3 and X4 are independently hydrogen, hydrocarbyl, substituted hydrocarbyl, or heteroaryl;
X5 is xe2x80x94X10, xe2x80x94OX10, xe2x80x94SX10, xe2x80x94NX8X10, or xe2x80x94SO2X11;
X6 is hydrocarbyl, substituted hydrocarbyl, heteroaryl, hydroxy protecting group or a functional group which increases the water solubility of the taxane derivative;
X7 is hydrocarbyl, substituted hydrocarbyl, heteroaryl, or sulfhydryl protecting group;
X8 is hydrogen, hydrocarbyl, or substituted hydrocarbyl;
X9 is an amino protecting group;
X10 is hydrocarbyl, substituted hydrocarbyl, or heteroaryl;
X11 is hydrocarbyl, substituted hydrocarbyl, heteroaryl, xe2x80x94OX10, or xe2x80x94NX8X14; and
X14 is hydrogen, hydrocarbyl, substituted hydrocarbyl, or heteroaryl.
Selective C(10) Derivatization
In accordance with the process of the present invention, it has been discovered that the C(10) hydroxyl group of a taxane can be selectively acylated in the absence of an amine base. Preferably, therefore, amine bases such as pyridine, triethylamine, dimethylaminopyridine and 2,6-lutidine, if present at all, are present in the reaction mixture in relatively low concentration. Stated another way, if an amine base is present in the reaction mixture, the molar ratio of the amine base to the taxane is preferably less than 1:1, more preferably less than 10:1, and most preferably less than 100:1.
Acylating agents which may be used for the selective acylation of the C(10) hydroxyl group of a taxane include anhydrides, dicarbonates, thiodicarbonates, and isocyanates. In general, the anhydrides, dicarbonates, and thiodicarbonates correspond to structure 4 and the isocyanates correspond to structure 5: 
wherein R1 is xe2x80x94ORa, xe2x80x94SRa, or Ra; R2 is xe2x80x94OC(O)Rb, xe2x80x94OC(O)ORb, xe2x80x94OC(O)SRb, xe2x80x94OPORbRc, or xe2x80x94OS(O)2Rb; R3 is hydrocarbyl, substituted hydrocarbyl, or heteroaryl; and Ra, Rb, Rc are independently hydrocarbyl, substituted hydrocarbyl, or heteroaryl. For example, suitable carboxylic acid anhydride acylating agents include acetic anhydride, chloroacetic anhydride, propionic anhydride, benzoic anhydride, and other carboxylic acid anhydrides containing substituted or unsubstituted hydrocarbyl or heteroaryl moieties; suitable dicarbonate acylating reagents include dibenzyl dicarbonate, diallyl dicarbonate, dipropyl dicarbonate, and other dicarbonates containing substituted or unsubstituted hydrocarbyl or heteroaryl moieties; and suitable isocyanate acylating agents include phenyl isocyanate, and other isocyanates containing substituted or unsubstituted hydrocarbyl or heteroaryl moieties. In addition, although the anhydrides, dicarbonates, and thiodicarbonates used as acylating agents may be mixed, it is generally preferred that they be symmetrical; that is, R1 and R2 are selected such that the molecule is symmetrical (e.g., if R1 is Ra, R2 is xe2x80x94OC(O)Rb with Ra being the same as Rb).
While the acylation of the C(10) hydroxy group of the taxane will proceed at an adequate rate for many acylating agents, it has been discovered that the reaction rate may be increased by including a Lewis acid in the reaction mixture. The concentration of the Lewis acid appears not to be narrowly critical; experimental evidence obtained to date suggests it may be present in either a stoichiometric or a catalytic amount. In general, Lewis acids which may be used include triflates and halides of elements of groups IB, IIB, IIIB, IVB, VB, VIB, VIIB, VIII, IIIA, IVA, lanthanides, and actinides of the Periodic Table (American Chemical Society format). Preferred Lewis acids include zinc chloride, stannic chloride, cerium trichloride, cuprous chloride, lanthanum trichloride, dysprosium trichloride, and ytterbium trichloride. Zinc chloride or cerium trichloride is particularly preferred when the acylating agent is an anhydride or dicarbonate. Cuprous chloride is particularly preferred when the acylating agent is an isocyanate.
The solvent for the selective acylation is preferably an ethereal solvent such as tetrahydrofuran. Alternatively, however, other solvents such as ether or dimethoxyethane may be used.
The temperature at which the C(10) selective acylation is carried out is not narrowly critical. In general, however, it is preferably carried out at room temperature or higher in order for the reaction to proceed at a sufficiently high rate.
For purposes of illustration, acylating reactions involving dibenzyl dicarbonate, diallyl dicarbonate, acetic anhydride, chloroacetic anhydride and phenyl isocyanate are illustrated in Reaction Schemes 1 through 5 below. In this series of reaction schemes, the taxane which is selectively acylated at the C(10) position is 10-deacetylbaccatin III. It should be understood, however, that these reaction schemes are merely illustrative and that other taxanes having a C(10) hydroxy group, in general, and other 7,10-dihydroxytaxanes, in particular, may be selectively acylated with these and other acylating agents in accordance with the present invention. 
In another aspect of the present invention, the C(10) hydroxyl group of a taxane may be selectively silylated. In general, the silylating agent is selected from the group consisting of silylamides and bissilyamides. Preferred silylamides and bissilyamides correspond to structures 6 and 7, respectively: 
wherein RD, RE, RF, RG, and RH are independently hydrocarbyl, substituted hydrocarbyl, or heteroaryl. Preferably, the silylating agents are selected from the group consisting of tri(hydrocarbyl)silyl-trifluoromethylacetamides and bis tri(hydrocarbyl)-silyltrifluoromethylacetamides, with the hydrocarbyl moiety being substituted or unsubstituted alkyl or aryl. For example, the preferred silylamides and bissilylamides include N,O-bis-(trimethylsilyl)trifluoroacetamide, N,O-bis-(triethylsilyl)trifluoroacetamide, N-methyl-N-triethylsilyltrifluoroacetamide, and N,O-bis(t-butyldimethylsilyl)trifluoroacetamide.
The silylating agents may be used either alone or in combination with a catalytic amount of a base such as an alkali metal base. Alkali metal amides, such as lithium amide catalysts, in general, and lithium hexamethyldisilazide, in particular, are preferred.
The solvent for the selective silylation reaction is preferably an ethereal solvent such as tetrahydrofuran. Alternatively, however, other solvents such as ether or dimethoxyethane may be used.
The temperature at which the C(10) selective silylation is carried out is not narrowly critical. In general, however, it is carried out at 0xc2x0 C. or greater.
Selective C(10) silylation reactions involving N,O-bis(trimethylsilyl)trifluoroacetamide and N,O-bis(triethylsilyl)trifluoroacetamide are illustrated in Reaction Schemes 6 and 7 below. In these reaction schemes, the taxane which is selectively silylated at the C(10) position is 10-deacetylbaccatin III. It should be understood, however, that these reaction schemes are merely illustrative and that other taxanes, having a C(10) hydroxy group, in general, and other 7,10-dihydroxytaxanes, in particular, may be selectively silylated with these and other silylating agents in accordance with the present invention. 
After the C(10) hydroxyl group of a 7,10-dihydroxytaxane has been derivatized as described herein, the C(7) hydroxyl group can readily be protected or otherwise derivatized selectively in the presence of the C(1) and C(13) hydroxyl groups (and a C(14) hydroxy group, if present).
Selective C(7) Derivatization
Selective acylation of the C(7) hydroxyl group of a C(10) acylated or silylated taxane can be achieved using any of a variety of common acylating agents including, but not limited to, substituted and unsubstituted carboxylic acid derivatives, e.g., carboxylic acid halides, anhydrides, dicarbonates, isocyanates and haloformates. For example, the C(7) hydroxyl group of baccatin III, 10-acyl-10-deacetylbaccatin III or 10-trihydrocarbylsilyl-10-deacetyl baccatin III can be selectively acylated with dibenzyl dicarbonate, diallyl dicarbonate, 2,2,2-trichloroethyl chloroformate, benzyl chloroformate or another common acylating agent.
In general, acylation of the C(7) hydroxy group of a C(10) acylated or silylated taxane are more efficient and more selective than are C(7) acylations of a 7,10-dihydroxy taxane such as 10-DAB, i.e., once the C(10) hydroxyl group has been acylated or silylated, there is a significant difference in the reactivity of the remaining C(7), C(13), and C(1) hydroxyl groups (and the C(14) hydroxyl group, if present). These acylation reactions may optionally be carried out in the presence or absence of an amine base.
Examples of selective C(7) acylation of a taxane having an acylated or silylated C(10) hydroxy group are shown in Reaction Schemes 8 through 11. In these reaction schemes, the taxane which is selectively acylated at the C(7) position is baccatin III or 10-triethylsilyl-10-deacetylbaccatin III. It should be understood, however, that these reaction schemes are merely illustrative and that taxanes having other acyl and silyl moieties at C(10) as well as other substituents at other taxane ring positions may be selectively acylated at C(7) with these and other acylating agents in accordance with the present invention. 
Alternatively, the C(7) hydroxyl group of a C(10) acylated taxane derivative can be selectively protected using any of a variety of hydroxy protecting groups, such as acetal, ketal, silyl, and removable acyl protecting groups. For example, the C(7) hydroxyl group may be silylated using any of a variety of common silylating agents including, but not limited to, tri(hydrocarbyl)silyl halides and tri(hydrocarbyl)silyl triflates. The hydrocarbyl moieties of these compounds may be substituted or unsubstituted and preferably are substituted or unsubstituted alkyl or aryl. For example, the C(7) hydroxyl group of baccatin III can be selectively silylated using silylating agents such as tribenzylsilyl chloride, trimethylsilyl chloride, triethylsilyl chloride, dimethyl isopropylsilyl chloride, dimethyl phenylsilyl chloride, and the like.
In general, silylations of the C(7) hydroxy group of a C(10) acylated taxanes are more efficient and more selective than are silylations of a 7,10-dihydroxy taxane such as 10-DAB, i.e., once the C(10) hydroxyl group has been acylated, there is a significant difference in the reactivity of the remaining C(7), C(13), and C(1) hydroxyl groups (and the C(14) hydroxyl group, if present). The C(7) silylation reaction may be carried out under a wide range of conditions, including in the presence or absence of an amine base.
Examples of selective C(7) silylation of C(10) acylated taxanes are shown in Reaction Schemes 12 through 15. In these reaction schemes, the taxane which is selectively silylated at the C(7) position is baccatin III or another C(10)-acyloxy derivative of 10-deacetylbaccatin III. It should be understood, however, that these reaction schemes are merely illustrative and that other taxanes may be selectively silylated with these and other silylating agents in accordance with the present invention. 
Alternatively, the C(7) hydroxyl group of C(10) acylated taxanes can be selectively protected using any of a variety of common reagents including, but not limited to, simple acetals, ketals and vinyl ethers, in the presence of an acid catalyst. These reagents (whether acetal, ketal, vinyl ether or otherwise) are referred to herein as xe2x80x9cketalizing agentsxe2x80x9d and are described in xe2x80x9cProtective Groups in Organic Synthesisxe2x80x9d by T. W. Greene, John Wiley and Sons, 1981. The acid catalyst used may be an organic or inorganic acid, such as toluenesulfonic acid or camphorsulfonic acid, in at least a catalytic amount. For example, the C(7) hydroxyl group of baccatin III can be selectively ketalized using 2-methoxy propene. Other suitable reagents for the preparation of acetals and ketals include methyl vinyl ether, ethyl vinyl ether, tetrahydropyran, and the like.
Selective ketalization of the C(7) substituent of a C(10) acylated taxane is more efficient and more selective than it is with 10-DAB, i.e., once the C(10) hydroxyl group has been acylated, there is a large difference in the reactivity of the remaining C(7), C(13), and C(1) hydroxyl groups (and the C(14) hydroxyl group, if present).
An example of selective formation of a C(7) ketal from baccatin III is illustrated in Reaction Scheme 16. It should be understood, however, that this reaction scheme is merely illustrative and that other taxanes may be selectively ketalized with this and other ketalizing agents in accordance with the present invention. 
Under appropriate conditions, the C(7) hydroxyl group of a taxane further comprising a C(10) hydroxyl group can be selectively silylated. Advantageously, these silylations are not limited to silyl groups bearing alkyl substituents having three carbons or less.
In general, the C(7) hydroxyl group of a taxane can be selectively silylated with a silylating agent which includes the xe2x80x94SiRJRKRL moiety wherein RJ, RK and RL are independently substituted or unsubstituted hydrocarbyl or heteroaryl, provided that any substituents are other than hydroxyl. In one embodiment of the present invention, if each of RJ, RK and RL is alkyl, then at least one of RJ, RK, and RL comprises a carbon skeleton (i.e., carbon chain or ring(s)) having at least four carbon atoms. Suitable silylating agents include silyl halides and silyl triflates, for example, tri(hydrocarbyl)silyl halides and tri(hydrocarbyl)silyl triflates. The hydrocarbyl substituents of these silylating agents may be substituted or unsubstituted and preferably are substituted or unsubstituted alkyl or aryl.
The selective silylation of the C(7) hydroxy group may be carried out in a solvent, such as dimethyl formamide (xe2x80x9cDMFxe2x80x9d) or pyridine and in the presence of an amine base, such as imidazole or pyridine. Reaction Schemes 17-20 illustrate the silylation of the C(7) hydroxy group of 10-DAB in high yield by treating 10-DAB with t-butyldimethylsilyl chloride, tribenzylsilyl chloride, dimethyl-isopropylsilyl chloride, and dimethylphenylsilyl chloride, respectively. Silylation under these conditions was surprising in view of the report by Denis, et. al. (J. Am. Chem. Soc., 1988, 110, 5917) that selective formation of 7-TBS-10-DAB was not possible. 
The process of the present invention can also be used to protect the C(7) and C(10) hydroxy groups of a 7,10-dihydroxytaxane with different silyl protecting groups. By selecting groups which can be removed under different conditions, the C(7) and C(10) hydroxy groups can be separately accessed for derivatization. These reactions, therefore, increase the flexibility of the overall process and, enable a higher yield for many of the individual protecting reactions relative to the yield obtained using currently available processes. For example, the triethylsilyl protecting group is more readily removed from C(10) than is the t-butyldimethylsilyl protecting group from C(7) and the dimethylphenylsilyl protecting group is more readily removed from C(7) than is the t-butyldimethylsilyl protecting group from C(10). The preparation of 7-t-butyldimethylsilyl-10-triethylsilyl-10-DAB and 7-dimethylphenylsilyl-10-t-butyldimethylislyl-10-DAB are illustrated in Reaction Schemes 21 and 22. 
The methods disclosed herein may be used in connection with a large number of different taxanes obtained from natural or synthetic sources to prepare a wide variety of taxane intermediates which may then be further derivatized. For example, the methods of the present invention may be effectively used to protect the C(7) and/or C(10) hydroxy functional group prior to the coupling reaction between a C(13) side chain precursor and a taxane to introduce a C(13) xcex2-amido ester side chain, and also prior to the reactions for preparing taxanes having alternative substituents at various locations on the taxane nucleus.
The attachment of a C(13) side chain precursor to a taxane may be carried out by various known techniques. For example, a side chain precursor such as an appropriately substituted xcex2-lactam, oxazoline, oxazolidine carboxylic acid, oxazolidine carboxylic acid anhydride, or isoserine derivative may be reacted with a tricyclic or tetracyclic taxane having a C(13) hydroxy, metallic oxide or ammonium oxide substituent to form compounds having a xcex2-amido ester substituent at C(13) as described, for example, Taxol: Science and Applications, M. Suffness, editor, CRC Press (Boca Rotan, Fla.) 1995, Chapter V, pages 97-121. For example, the synthesis of taxol from 10-DAB is illustrated in reaction scheme 23. It should be noted that while a xcex2-lactam and 10-DAB are used in this reaction scheme, other side chain precursors and other taxanes could be substituted therefor without departing from the present invention. 
The process illustrated in Reaction Scheme 23 is significantly more efficient than any other currently known process, due to the high yields and selectivity of the cerium trichloride catalyzed acetylation of the C(10) hydroxyl group of 10-DAB and the subsequent silylation of the C(7) hydroxyl group. The synthesis proceeds in four steps and 89% overall yield.
Reaction schemes 24 and 25 illustrate the preparation of taxanes having substituents appended to the C(7) hydroxyl group and a free C(10) hydroxyl group. The method of the current invention provides flexibility so that the substituent attached to the C(7) hydroxyl group can be put in place either before or after attachment of the C(13) side chain.
Reaction scheme 24 outlines the preparation of a taxane which has been found to be a potent chemotherapeutic radiosensitizer, illustrating attachment of the substituent at the C(7) hydroxyl group before introduction of the C(13) side chain. According to the process of reaction scheme 7,10-DAB is first converted to 10-TES-10-DAB. The C(7) hydroxyl group is then converted to an intermediate imidazolide by treatment with carbonyl diimidazole, and the intermediate imidazolide subsequently reacts, without isolation, with metronidazole alcohol to provide 7-metro-10-TES-10-DAB. Coupling of 7-metro-10-TES-10-DAB with a xcex2-lactam to introduce the side chain at C(13) is followed by removal of the TES groups at C(10) and C(2xe2x80x2) by treatment with HF and pyridine. 
Reaction scheme 25 outlines the preparation of a taxane useful in identifying proteins which form bioconjugates with taxanes. It illustrates a protocol for attachment of a substituent at the C(7) hydroxyl group after introduction of the C(13) side chain. According to the processes of reaction schemes 7 and 11, 10-DAB is first converted to 7-p-nitrobenzyloxycarbonyl-10-TES-10-DAB. The C(13) side chain is attached employing a TES protected xcex2-lactam, and the p-nitrobenzyloxycarbonyl protecting group is then selectively removed by treatment with hydrogen and a palladium catalyst, producing 2xe2x80x2,10-(bis)-TES-taxotere. The C(7) hydroxyl group then reacts with carbonyl diimidazole and the derived imidazolide is treated with 1,4-diamino butane to give a primary amine. Reaction of the primary amine with the hydroxysuccinimide ester of biotin completes the attachment of the biotinamide group at C(7). Finally, treatment with HF in pyridine solution removes the TES protecting groups at C(10) and C(2xe2x80x2). 
The protected taxane derivatives or the intermediates or starting materials used in the preparation of such protected taxane derivatives can be further modified to provide for alternative substituents at various positions of the taxane.
Taxanes having C(2) and/or C(4) substituents other than benzoyloxy and acetoxy, respectively, can be prepared from baccatin III, 10-DAB and other taxanes as more fully described in PCT Patent Application WO 94/01223. In general, the C(2) and C(4) acyloxy substituents are treated with lithium aluminum hydride or another suitable reducing agent to from hydroxy groups at C(2) and C(4) which may then be reacted, for example, with carboxylic acid halides (optionally after protection of the C(2) hydroxy group together with the C(1) hydroxy group with a 1,2-carbonate protecting group) to obtain the desired C(2) and C(4) derivatives.
Taxanes having C(7) substituents other than hydroxy and acyloxy as described herein can be prepared from baccatin III, 10-DAB, and other taxanes as more fully described in PCT Patent Application WO 94/17050. For example, a C(7) xanthate may be subjected to tin hydride reduction to yield the corresponding C(7) dihydro taxane. Alternatively, C(7) fluoro-substituted taxanes can be prepared by treatment of C(13)-triethylsilyl-protected baccatin III with 2-chloro-1,1,2-trifluorotriethylamine at room temperature in THF solution. Other baccatin derivatives with a free C(7) hydroxyl group behave similarly. Alternatively, 7-chloro baccatin III can be prepared by treatment of baccatin III with methanesulfonyl chloride and triethylamine in methylene chloride solution containing an excess of triethylamine hydrochloride.
Taxanes having C(9) substituents other than keto can be prepared from baccatin III, 10-DAB and other taxanes as more fully described in PCT Patent Application WO 94/20088. In general, the C(9) keto substituent of the taxane is selectively reduced to yield the corresponding C(9) xcex2-hydroxy derivative with a borohydride, preferably tetrabutylammonium borohydride (Bu4NBH4) or triacetoxy-borohydride. The C(9) xcex2-hydroxy derivative can then be protected at C(7) with a hydroxy protecting group and the C(9) hydroxy group can be acylated following the methods described herein for acylation of the C(7) hydroxy group. Alternatively, reaction of 7-protected-9xcex2-hydroxy derivative with KH causes the acetate group (or other acyloxy group) to migrate from C(10) to C(9) and the hydroxy group to migrate from C(9) to C(10), thereby yielding a 10-desacetyl derivative, which can be acylated as described elsewhere herein.
Taxanes having C(10) substituents other than hydroxy, acyloxy or protected hydroxy as described herein may be prepared as more fully described in PCT Patent Application WO 94/15599 and other literature references. For example, taxanes having a C(10) keto substituent can be prepared by oxidation of 10-desacetyl taxanes. Taxanes which are dihydro substituted at C(10) can be prepared by reacting a C(10) hydroxy or acyloxy substituted taxane with samarium diiodide.
Taxanes having a C(14) substituent other than hydrogen may also be prepared. The starting material for these compounds may be, for example, a hydroxylated taxane (14-hydroxy-10-deacetylbaccatin III) which has been discovered in an extract of yew needles (CandEN, p 36-37, Apr. 12, 1993). Derivatives of this hydroxylated taxane having the various C(2), C(4), C(7), C(9), C(10), C3xe2x80x2 and C5xe2x80x2 functional groups described above may also be prepared by using this hydroxylated taxane. In addition, the C(14) hydroxy group together with the C(1) hydroxy group of 10-DAB can be converted to a 1,2-carbonate as described in CandEN or it may be converted to a variety of esters or other functional groups as otherwise described herein in connection with the C(2), C(4), C(9) and C(10) substituents.
The process of the present invention thus enables the preparation of taxanes having the following structure: 
wherein
M comprises ammonium or is a metal;
R1 is hydrogen, hydroxy, protected hydroxy, or together with R14 or R2 forms a carbonate;
R2 is keto, xe2x80x94OT2, acyloxy, or together with R1 forms a carbonate;
R4 is xe2x80x94OT4 or acyloxy;
R7 is hydrogen, halogen, xe2x80x94OT7, or acyloxy;
R9 is hydrogen, keto, xe2x80x94OT9, or acyloxy;
R10 is hydrogen, keto, xe2x80x94OT10, or acyloxy;
R7, R9, and R10 independently have the alpha or beta stereochemical configuration;
R13 is hydroxy, protected hydroxy, keto, MOxe2x80x94 or 
xe2x80x83R14 is hydrogen, xe2x80x94OT14, acyloxy, or together with R1 forms a carbonate;
T2, T4, T7, T9, T10 and T14 are independently hydrogen or hydroxy protecting group;
X1 is xe2x80x94OX6, xe2x80x94SX7, or xe2x80x94NX8X9;
X2 is hydrogen, hydrocarbyl, substituted hydrocarbyl, or heteroaryl;
X3 and X4 are independently hydrogen, hydrocarbyl, substituted hydrocarbyl, or heteroaryl;
X5 is xe2x80x94X10, xe2x80x94OX10, xe2x80x94SX10, xe2x80x94NX8X10, or xe2x80x94SO2X11;
X6 is hydrogen, hydrocarbyl, substituted hydrocarbyl, heteroaryl, hydroxy protecting group, or a functional group which increases the water solubility of the taxane derivative;
X7 is hydrocarbyl, substituted hydrocarbyl, heteroaryl, or sulfhydryl protecting group;
X8 is hydrogen, hydrocarbyl, or substituted hydrocarbyl;
X9 is an amino protecting group;
X10 is hydrocarbyl, substituted hydrocarbyl, or heteroaryl;
X11 is hydrocarbyl, substituted hydrocarbyl, heteroaryl, xe2x80x94OX10, or xe2x80x94NX8X14;
X14 is hydrogen, hydrocarbyl, substituted hydrocarbyl, or heteroaryl.
In one embodiment of the present invention, the substituents of the taxane (other than the C(7), C(10) and C(13) substituents) correspond to the substituents present on baccatin III or 10-DAB. That is, R14 is hydrogen, R9 is keto, R4 is acetoxy, R2 is benzoyloxy, and R1 is hydroxy. In other embodiments, the taxane has a structure which differs from that of taxol or Taxotere(copyright) with respect to the C(13) side chain and at least one other substituent. For example, R14 may be hydroxy; R2 may be hydroxy, xe2x80x94OCOZ2 or xe2x80x94OCOOZ22 wherein Z2 is hydrogen, hydrocarbyl, substituted hydrocarbyl, or heteroaryl and Z22 is hydrocarbyl, substituted hydrocarbyl, or heteroaryl; R4 may be hydroxy, xe2x80x94OCOZ4 or xe2x80x94OCOOZ44 wherein Z4 is hydrogen, hydrocarbyl, substituted hydrocarbyl, or heteroaryl and Z44 is hydrocarbyl, substituted hydrocarbyl, or heteroaryl; R7 may be hydrogen, hydroxy, xe2x80x94OCOZ7 or xe2x80x94OCOOZ77 wherein Z7 is hydrogen, hydrocarbyl, substituted hydrocarbyl, or heteroaryl and Z77 is hydrogen, hydrocarbyl, substituted hydrocarbyl, or heteroaryl, R9 may be hydrogen, hydroxy, xe2x80x94OCOZ9 or xe2x80x94OCOOZ99 wherein Z9 is hydrogen, hydrocarbyl, substituted hydrocarbyl, or heteroaryl and Z99 is hydrogen, hydrocarbyl, substituted hydrocarbyl, or heteroaryl, and R10 may be hydrogen, hydroxy, xe2x80x94OCOZ10 or xe2x80x94OCOOZ1010 wherein Z10 is hydrogen, hydrocarbyl, substituted hydrocarbyl, or heteroaryl and Z1010 is hydrogen, hydrocarbyl, substituted hydrocarbyl, or heteroaryl.
In a preferred embodiment, the taxane has the formula 
wherein P10 is acyl, said acyl comprising at least three carbon atoms or two carbon atoms and a nitrogen, oxygen or sulfur atom. Stated another way, xe2x80x94OP10 is other than acetoxy. More preferably, P10 is xe2x80x94(Cxe2x95x90O)RA, xe2x80x94(Cxe2x95x90O)ORB, or xe2x80x94(Cxe2x95x90O)NRC wherein RA is substituted or unsubstituted hydrocarbyl or heteroaryl, said unsubstituted hydrocarbyl comprising at least two carbon atoms; RB and RC are independently substituted or unsubstituted hydrocarbyl. Still more preferably, RA is substituted or unsubstituted alkyl or aryl, said unsubstituted alkyl comprising at least two carbon atoms; and RB and RC are independently substituted or unsubstituted alkyl or aryl.
In another embodiment of the invention, the taxane has the formula 
wherein P7 and P10 are independently substituted or unsubstituted acyl. In this embodiment, P7 and P10 are preferably different.
Definitions
As used herein, the terms xe2x80x9cselectivexe2x80x9d and xe2x80x9cselective derivatizationxe2x80x9d shall mean that the desired product is preferentially formed over any other by-product. Preferably, the desired product is present in a molar ratio of at least 9:1 relative to any other by-product and, more preferably, is present in a molar ratio of at least 20:1 relative to any other by-product.
In addition, xe2x80x9cPhxe2x80x9d means phenyl; xe2x80x9cBzxe2x80x9d means benzoyl; xe2x80x9cBnxe2x80x9d means benzyl; xe2x80x9cMexe2x80x9d means methyl; xe2x80x9cEtxe2x80x9d means ethyl; xe2x80x9ciPrxe2x80x9d means isopropyl; xe2x80x9ctBuxe2x80x9d and xe2x80x9ct-Buxe2x80x9d means tert-butyl; xe2x80x9cAcxe2x80x9d means acetyl; xe2x80x9cTESxe2x80x9d means triethylsilyl; xe2x80x9cTMSxe2x80x9d means trimethylsilyl; xe2x80x9cTBSxe2x80x9d means Me2t-BuSixe2x80x94; xe2x80x9cCDIxe2x80x9d means carbonyl diimidazole; xe2x80x9cBOMxe2x80x9d means benzyloxymethyl; xe2x80x9cDBUxe2x80x9d means diazabicycloundecane; xe2x80x9cDMAPxe2x80x9d means p-dimethylamino pyridine; xe2x80x9cLHMDSxe2x80x9d or xe2x80x9cLiHMDSxe2x80x9d means lithium hexamethyldisilazide; xe2x80x9cDMFxe2x80x9d means dimethylformamide; xe2x80x9c10-DABxe2x80x9d means 10-desacetylbaccatin III; xe2x80x9cCbzxe2x80x9d means benzyloxycarbonyl; xe2x80x9cAllocxe2x80x9d means allyloxycarbonyl; xe2x80x9cTHFxe2x80x9d means tetrahydrofuran; xe2x80x9cBOCxe2x80x9d means benzyloxycarbonyl; xe2x80x9cPNBxe2x80x9d means para-nitrobenzyl; xe2x80x9cTrocxe2x80x9d means 2,2,2-trichloroethoxycarbonyl; xe2x80x9cEtOAcxe2x80x9d means ethyl acetate; xe2x80x9cTHFxe2x80x9d means tetrahydrofuran; xe2x80x9cprotected hydroxylxe2x80x9d means xe2x80x94OP wherein P is a hydroxyl protecting group; and xe2x80x9chydroxyl protecting groupxe2x80x9d includes, but is not limited to, acetals having two to ten carbons, ketals having two to ten carbons, and ethers, such as methyl, t-butyl, benzyl, p-methoxybenzyl, p-nitrobenzyl, allyl, trityl, methoxymethyl, methoxyethoxymethyl, ethoxyethyl, methoxy propyl, tetrahydropyranyl, tetrahydrothiopyranyl; and trialkylsilyl ethers such as trimethylsilyl ether, triethylsilyl ether, dimethylarylsilyl ether, triisopropylsilyl ether and t-butyldimethylsilyl ether; esters such as benzoyl, acetyl, phenylacetyl, formyl, mono-, di-, and trihaloacetyl such as chloroacetyl, dichloroacetyl, trichloroacetyl, trifluoroacetyl; and carbonates including but not limited to alkyl carbonates having from one to six carbon atoms such as methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl; isobutyl, and n-pentyl; alkyl carbonates having from one to six carbon atoms and substituted with one or more halogen atoms such as 2,2,2-trichloroethoxymethyl and 2,2,2-trichloroethyl; alkenyl carbonates having from two to six carbon atoms such as vinyl and allyl; cycloalkyl carbonates having from three to six carbon atoms such as cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl; and phenyl or benzyl carbonates optionally substituted on the ring with one or more C1-6 alkoxy, or nitro. Other hydroxyl protecting groups may be found in xe2x80x9cProtective Groups in Organic Synthesisxe2x80x9d by T. W. Greene, John Wiley and Sons, 1981, and Second Edition, 1991.
The xe2x80x9chydrocarbonxe2x80x9d and xe2x80x9chydrocarbylxe2x80x9d moieties described herein are organic compounds or radicals consisting exclusively of the elements carbon and hydrogen. These moieties include alkyl, alkenyl, alkynyl, and aryl moieties. These moieties also include alkyl, alkenyl, alkynyl, and aryl moieties substituted with other aliphatic or cyclic hydrocarbyl groups, and include alkaryl, alkenaryl and alkynaryl. Preferably, these moieties comprise 1 to 20 carbon atoms.
The alkyl groups described herein are preferably lower alkyl containing from one to six carbon atoms in the principal chain and up to 20 carbon atoms. They may be straight, branched chain or cyclic and include methyl, ethyl, propyl, isopropyl, butyl, hexyl and the like. They may be substituted with aliphatic or cyclic hydrocarbyl radicals.
The alkenyl groups described herein are preferably lower alkenyl containing from two to six carbon atoms in the principal chain and up to 20 carbon atoms. They may be straight or branched chain and include ethenyl, propenyl, isopropenyl, butenyl, isobutenyl, hexenyl, and the like. They may be substituted with aliphatic or cyclic hydrocarbyl radicals.
The alkynyl groups described herein are preferably lower alkynyl containing from two to six carbon atoms in the principal chain and up to 20 carbon atoms. They may be straight or branched chain and include ethynyl, propynyl, butynyl, isobutynyl, hexynyl, and the like. They may be substituted with aliphatic or cyclic hydrocarbyl radicals.
The aryl moieties described herein contain from 6 to 20 carbon atoms and include phenyl. They may be hydrocarbyl substituted with the various substituents defined herein. Phenyl is the more preferred aryl.
The heteroaryl moieties described are heterocyclic compounds or radicals which are analogous to aromatic compounds or radicals and which contain a total of 5 to 20 atoms, usually 5 or 6 ring atoms, and at least one atom other than carbon, such as furyl, thienyl, pyridyl and the like. The heteroaryl moieties may be substituted with hydrocarbyl, heterosubstituted hydrocarbyl or hetero-atom containing substituents with the hetero-atoms being selected from the group consisting of nitrogen, oxygen, silicon, phosphorous, boron, sulfur, and halogens. These substituents include hydroxy; lower alkoxy such as methoxy, ethoxy, butoxy; halogen such as chloro or fluoro; ethers; acetals; ketals; esters; heteroaryl such as furyl or thienyl; alkanoxy; acyl; acyloxy; nitro; amino; and amido.
The substituted hydrocarbyl moieties described herein are hydrocarbyl moieties which are substituted with at least one atom other than carbon and hydrogen, including moieties in which a carbon chain atom is substituted with a hetero atom such as nitrogen, oxygen, silicon, phosphorous, boron, sulfur, or a halogen atom. These substituents include hydroxy; lower alkoxy such as methoxy, ethoxy, butoxy; halogen such as chloro or fluoro; ethers; acetals; ketals; esters; heteroaryl such as furyl or thienyl; alkanoxy; acyl; acyloxy; nitro; amino; and amido.
The acyl moieties and the acyloxy moieties described herein contain hydrocarbyl, substituted hydrocarbyl or heteroaryl moieties. In general, they have the formulas xe2x80x94C(O)G and xe2x80x94OC(O)G, respectively, wherein G is substituted or unsubstituted hydrocarbyl, hydrocarbyloxy, hydrocarbylamino, hydrocarbylthio or heteroaryl.
The ketal moieties described herein have the general formula 
wherein X31, X32, X33 and X34 are independently hydrocarbyl, substituted hydrocarbyl or heteroaryl moieties. They may be optionally substituted with the various substituents defined herein. The ketal moieties are preferably substituted or unsubstituted alkyl or alkenyl, and more preferably substituted or unsubstituted lower (C1-C6) alkyl. These ketal moieties additionally may encompass sugars or substituted sugars and include ketal moieties prepared from sugars or substituted sugars such as glucose and xylose. When a ketal moiety is incorporated into a taxane of the present invention as a C(7) hydroxy protecting group, then either X31 or X32 represents the taxane moiety.
The acetal moieties described herein have the general formula 
wherein X31, X32 and X33 are independently hydrocarbyl, substituted hydrocarbyl or heteroaryl moieties. They may be optionally substituted with the various substituents defined herein other than hydroxyl. The acetal moieties are preferably substituted or unsubstituted alkyl or alkenyl, and more preferably substituted or unsubstituted lower (C1-C6) alkyl. These acetal moieties additionally may encompass sugars or substituted sugars and include acetal moieties prepared from sugars or substituted sugars such as glucose and xylose. When an acetal moiety is incorporated into a taxane of the present invention as a C(7) hydroxy protecting group, then either X31 or X32 represents the taxane moiety.
The term xe2x80x9ctaxanexe2x80x9d as used herein, denotes compounds containing the A, B and C rings (with numbering of the ring positions shown herein): 